In May 1990, five shipping containers holding approximately 80,000 pairs of Nike shoes fell off a freighter during a storm in the North Pacific. About 200 days later, some of these shoes began to wash up on beaches from Canada down to Oregon.
But as beachcombers collected and compared the shoes, they noticed something odd. On beaches up north, in Canada and Washington, almost all the shoes were right-footed; whereas further south in Oregon, most of the shoes were left-footed.
Skye Moody explains why this was so in her book Washed Up: The Curious Journeys of Flotsam and Jetsam
The slight toe curvature of left- and right-footed shoes caused the right-footed shoes to tack northeastward into the Alaska Current, passing the Queen Charlottes along the way, where many beached. Meanwhile, the left-footed Nikes tacked snugly into the southeast-bound California Current, and as it passed Oregon, were caught on an incoming tide.
Drift pattern of Nike shoes
image source: The Nike Shoe Investigation
Oceanographer Curtis Ebbesmeyer co-authored an academic paper about the 1990 shoe spill ("Shoe spill in the North Pacific"
-- unfortunately behind a paywall). It also inspired him to start studying other ocean flotsam, such as rubber duckies, as a way to gain info about currents. He calls this study 'flotsametrics
'. He also occasionally puts out a Beachcombers' Alert Newsletter